The invention relates to pigment preparations which are covered with a new kind of resin base and which when used as printing inks for offset printing exhibit improved rheological properties.
It is known that resinated pigments possess enhanced color strength, gloss, transparency and good dispersibility in the application medium for offset printing inks.
Simple natural resins based on rosin have been found to be particularly suitable for pigment preparation. Rosin consists of a mixture of various resin acids, predominantly abietic acid, pimaric acid and derivatives thereof. Resins based on rosin are often modified chemically owing to their sensitivity to oxidation, such modification being brought about, for example, by disproportionation or hydrogenation. These chemical derivatives of the natural resin acids possess an average molar mass of about 300 g mol.sup.-1. These resin types are therefore referred to as low molecular mass resins. However, when used in modern offset printing inks, the pigments prepared with these rosin derivatives have a tendency to mist. Misting means that, in the roll nips of modem, high-speed offset rotary presses, especially between the inking rollers and the printing plate cylinder, the printing ink tends to form an aerosol. The aerosol comes about through the breakup of threads of printing ink which are formed in the course of the spreading of the printing ink on the exit side of the roll nips. The fine ink mist soils the printing presses and pollutes the ambient air.